Inhibited phosphoric acid solution



Patented Sept. 20, 1949 r. p

UNITED- ;PATENT INIDBITEDEBHOSPHOMC A6112) iSGLUmIQN rais n-nuns. maasnesesnr 'No Drawing. ApplicationiFeln-nanyaii,51846,

"'SerialNo.(i4s6;480-.

(Q1l@nt d under the act .of 'March 1883, as I amended April 30, 19%;.3'10 10. .Gfiil 57i) This invention relates to l inhibitonsrior th steel. *nrsenic pentoxide "proved to be a ;v ery eon-Sion r t bnasisl amdselsae s seil e isr inhi it p star ,s t gd 919 with inhibitors for phosphoric'acid solutions. posure -(up' to abgp t 433 hours) lout conversely Moreparticularly this invention includes a V hha ebii df fieabhemusnm quinoline composition -for aqueous phosphoric {for-longer ji g' qf gfi' ifi" ta r acid solutions -to inhibit -the corrosion of fer-rous pitting which 355 1 1 i i i. m t 1 l I n ment of pin holes inthe arsenicprot'ectivrllm It is the object of this invention to prepare on the surface of the metal. These pinholes ala composition which will inhibit the corrosion lowed acid to penetrate under the film and seriof metals by acids and to provide a process for 10 ous, localized, corrosion resulted even though preventing such corrosion. there was no visible evidence of attack until a Acids are used to a very great extent in manuclose examination was made of the metal after facturing processes and the problem of the corthe test piece had been removed from the acid rosion of metal equipment is always present. solution for cleaning and weighing at the end Iron and mild steel, which are relatively inof the test. .In one case, for example, the rate expensive cannot ordinarily be used where exof corrosion with AS205 inhibited solutions, when posure to acids is required. It is therefore necesexpressed as average penetration in inches per sary to inhibit the corrosive action of the acids month, or as grams per sq. cm. per hour, was or to provide expensive acid-resistant apparatus. very low, but one deep pit had formed on the Acids are also used in pickling solutions and test piece which was 1 6" to V in depth. inhibitors are required to prevent too violent an AS205 fails as an inhibitor because the protecattack on the base metal. tive film it forms on the surface of the metal In oil well cleaning, acids are eifective, but the apparently does not remain absolutely continuous well casings will be seriously attacked unless an for a very long time. Other types of compounds, inhibitor is employed. i. e., organic nitrogen and sulfur compounds, also There is one very serious disadvantage to the form films but of a different type, on steel; these use of acids such as HaPOw, from a manufacturing might be classed, for the sake of differentiation, standpoint. Solutions of the acid attack iron as physical or mechanical films, whereas the or mild steel very strongly, as would be expected, AS205 probably forms a chemical film through the iron going into solution and hydrogen gas reaction with iron. It was believed possible that being liberated. A few laboratory corrosion tests if both types of inhibitors were present in H3PO4- indicated that the rate of corrosion of mild steel solutions, the action of one might augment that by a 25% HaPO4 solution is about 2.7 inches per of the other, i. e., the physical or mechanical year penetration. This high rate obviously prefilms-forming compound might serve to repair cludes the use of ordinary steel equipment in 5 pin-holes which develop in the A5205 film. On processes employing phosphoric acid. It likewise the basis of this hypothesis, combinations of indicates the necessity of finding a satisfactory AS205 with several organic nitrogen and sulfur inhibitor for this corrosion in order to make compounds which showed appreciable inhibition H3Po4 pr esses m ra i a when used alone, were tried as inhibitors in 25% A search was started for a satisfactory inhib- 4( aqueous H3PO4. The only one which showed itor, most of the early work consisting of an great promise was a mixture of A5205 and evaluation of arsenic pentoxide (AS205) which 4-methyl-2-hydroxy quinoline. The data of Taother i est (Kosting & Heins, ble I show the results obtained with the inhibitor Chem. 23, 140 1931) had recommended as being combination in comparison with those obtained the best inhibitor for H3PO4 attack of iron and with each compound alone and with no inhibitor.

TABLE I Corrosion of mild steel by 25% aqueous H3P04 solutions at room temperature Inhibitor Average 5%; Pene- Condition of Test Piece at End Test Nature Cono. anon Percent days in./1no. I None I 2 0.120 Uniform attack; suriace rough; size 01 piece visibly reduced.

A5 0 0.2 43 0. 00433 Sagere pitting on edges of test pieces; some pits a eep.

A5105 0.4 1 46 0.00118 Severe pitting; one large pit Mo" deep.

4-methy1-2-hydrosy quinoline- 0. 2 1 22 0.00441 Uniform attack; no pitting. 52f j i 5gg g a figx: g: 46 0.00072 Slight discoloration of metal; no visible corrosion.

1 Test was stopped as soon as serious corrosion was noted.

Although the above description is limited to I claim: 1 4-methyl-2-hydroxy quinoline, the preferred in- A composition inhibited against corrosion of hibitor, and most effective in mixtures of arsenic ferrous metals by phosphoric acid and consisting pentoxide, other heterocyclicprganic nitrogen of,a, 25% aqueous H3PO4 solution containing .1% compounds may be used. 4-methyl-2-hydroxy 2513.5-AS205 and .1% of 4-methy1-2-hydroxy quincquinoline can be used alone or combined with line.

arsenic pentoxide to produce an improved 'in- FRANK E. DOLIAN. hibitor which will prevent the corrosion of metals, I

particularly ferrous metals, by acids. .Although REFERENCES CITED phosphoric acid specifically is disclosed, my in- The following references are of record in the .vention is applicable toinhibit corrosion of other file of this patent.

acids. 7

While my invention has been described with UNITED STATES A ENTS particular reference to specific embodiments it Number Name Date is to be understood that the above disclosure 1,678,775 Graven July 1928 is to be considered broadly, and limited solely 1,746,676 Rhodes j Feb. 11, 1930 by the Scope of the appended shim 1,377,504 Grebe et a1 Sept. 13,1932 

